Check valves are used in a variety of applications in fluid systems to allow for the unidirectional passage of upstream pressurized fluid, that is, pressurized fluid upstream of the outlet of a check valve, above a particular preselected threshold pressure level. Check valves of the expandable o-ring style type can include an elastomeric ring that can be mounted on a conical shaped tapered surface of a valve. The elastomeric ring usually has a memory shape and is mounted to constrict the tapered surface, causing the ring to be biased to a normal position on the tapered surface that has a smaller cross sectional diameter. When the elastomeric ring is in this normal position, the ring normally seals against the valve body to prevent the flow of fluid through the valve.
If fluid pressure downstream from the elastomeric ring is greater than fluid pressure upstream from the ring, the downstream pressure along with the bias of the elastomeric ring will cause the ring to return to the normal position, closing the valve. The check valve will also remain closed if upstream fluid pressure is greater than downstream pressure unless the upstream pressure exerts a total force against the elastomeric ring that is greater than a predetermined cracking force, opening the valve. The predetermined cracking pressure is typically dependent on the total biasing force of the ring's memory shape and the amount of surface area of the ring that is exposed to fluid pressure at a given time.
Expandable o-ring style check valves are desirable to use since they have an inherent advantage in that a check valve spring and sealing member are usually combined into a single elastomeric ring component. However, where a single elastomeric ring is used both as a valve spring and sealing member, a ring material must be selected that can allow the ring to perform adequately both in spring actuation and sealing capacities. It follows that the use of a single elastomeric ring may not allow for the use of ring shapes and materials optimal for both spring actuation and sealing.